Forrest et al. (2004) presented 5-30 micron Spitzer Infrared
Spectrograph observations of six SED Class II YSO's in
Taurus. All of the sources have broad 10 micron silicate
emission features. Each one has a unique shape, indicating
variation in composition and crystallinity of the silicate
grains in the circumstellar disks of these 6 YSO's. One of
the sources, CoKu Tau /4, which apparently has very little
disk material out to ~10 AU, has a very smooth and narrow 10
micron emission feature, indicating the silicate grains
composing its disk are amorphous and simple. The spectra of
the other five sources, all of which have accretion disks
with inner radii much less than ~1 AU, have more complicated
10 micron features, indicating the presence of crystalline
silicates, which are believed to arise from processing of
amorphous silicates. This processing apparently has not
occurred for CoKu Tau /4, where the observable dust is cool
(~122 K). The dust emissivity is derived from the observed
spectra and compared to grain models. For CoKu Tau /4, small
amorphous spherical olivine grains are indicated. For the
sources with more complexity (FM Tau, IP Tau, GG Tau, FN
Tau, and CY Tau in order of complexity), additional
components of crystalline forsterite, enstatite, and larger
grains are needed to fit the spectra.

This work is based on observations made with the Spitzer
Space Telescope, which is operated by the Jet Propulsion
Laboratory, California Institute of Technology under NASA
contract 1407. Support for this work was provided by NASA
through contract number 1257184 issued by JPL/Caltech and
the Spitzer Fellowship Program, under award 011 808-001.